The present invention relates generally to a CMOS analog-to-digital converter (ADC) and a temperature sensing device using the converter, and more particularly to an apparatus for converting an analog voltage or temperature to a digital signal by using voltage controlled oscillators (VCOs) and counters.
To enable a digital system to perform environmental monitoring and processing, it is necessary to convert an analog signal such as supply voltage or temperature to a digital signal. To convert analog voltage signals into digital signals, the "sample and convert" approach is utilized in conventional technologies, in which complicated circuits and larger areas are required. To achieve temperature sensing, thermal resistors, which are not compatible with the standard CMOS digital IC manufacturing process and are not adapted for monolithic structures, are employed.
Sigma-Delta conversion is an advanced analog/digital conversion technique developed in recent years. It utilizes low resolution oversampling of analog signals, and then employs feedback and digital filtering techniques to convert the presentation with a high sampling rate but low accuracy into the presentation with a low sampling rate but high accuracy; parametric requirements of the analog circuit are thereby reduced at the expense of circuit complexity and device size.
The aforementioned conventional technologies are disadvantageous in circuit complexity, wafer area and manufacturing cost, which can be improved dramatically by utilizing the fact that supply voltages and environmental temperatures are all slow-varying analog signals.